Purification of tetrahydro



Sept. 4, 1951 A. D. GREEN ETAL PURIFICATION OF TETRAHYDROPHTHALIMIDES Filed Sept. 20. 1949 doku/d lllll.

l N CuDOnclZOd geeni r'rze allesl Kzltlegn. Inventors bg mwa# M Clbbo'rneg Patented Sept. 4, 1951 'i PURIFICATION OF TETRAHYDRO- PHTHALIMIDES- Arthur D. Green, Ernest O. Ohsol, and Allen Kittleson, Cranford, N. J., assignors to Standard Oil Development Company, a corporation of Delaware Application September 20,

9 Claims. l

This invention. relates tov a process for the purication. ofA tetrahydrophthalimides and more particularly to the purification of tetrahydrophthalimides for their use in the preparation of N-thiotrichloromethyl tetrahydrophthalimides.

N thiotrichloitomethyl V(or N trichloromethylthio)` tetrahydrophthalimides are disclosedin.U,.S, application Serial No. 90,271, filed April 28, 1949, now Patent No. 2,553,770, as eX- tremely eiective parasiticides and especially ef#- fective ungicides.

These compounds are prepared by dissolving the desired imide,r in. an aqueous alkaline solution, followed by addition of about an equal molecular quantity of perchloromethyl mercaptan. The mixture is stirred rapidly, conveniently, until the aqueous medium becomes acid to litmus, then filtered to obtain the product whichcan be air dried. The reaction may be carried out at room temperature. In cases Where the imide is readily hydrolyzed' in alkaline solution, it may be advantageous to cool the reaction mixture as low as C.

The metal compound'used to supply the necessary alkaline solution is a compound ofv an alkali metal, such as lithium, sodium and potassium, and'the like. Because of cost' factors, sodium and potassium arepreferred. The alkali is pres'- ent preferablyr in amounts equivalent to the imide used. While other basic compounds may be* used, it is desirable to use the alkali hydroxidesbecause of the consequent avoidance of the presence of other anionradicals which might have to' be removed.

Variations onthese procedures can be made, of course'. Thus the alkali metal imide salts, if available, canbe dissolved directly in water and the process-further carried on as indicated above for the aqueoussolution reaction.

N-thiotrichloromethyl tetrahydrophthalimide, which isillustrated by Formula I. below c Hf \o 2Formula I employs tetrahydrophthalimide as the starting material.

In the manufacture of tetrahydrophthalimide, the nal step usually comprises heating a melt of tetrahydrophthalimide toA a temperature in A 1949, seria1Nm 116,664

the range oft 204? to 260 C, to convert amides or ammonium salts to the imide. Invconventional methods of subsequent, isolation of the desired tetrahydrophthalimidev product, the melt is cooled, solidified, broken up, ground to a powder, and puried by recrystallization from a sol.- Vent such as acetone or alcohol. The hot melt is also sometimesl distilledlunder, high vacuumr to take overhead a'pure imide out eitheras a molten distillate or as aA solid sublimate.` In each.case, there still remainsa. rather. expensive and cum.- bersome stepof cooling hot melt or. solids, crushing. and. grinding. l

in addition, it has been found. thatv crude tetrahydrophthalimide contains as. an impurity anA ingredient which actually poisons and inhibits the subsequent, reaction of. the imide with perchloromethyl. mercaptan.`

Thel present inventionis an improved method for the purification of tetrahydrophthalimides which is ideally adapted to overcome the beforementioned difficulties. The method comprises injecting crude hot molten tetrahydrophthal.-r

imide into anV aqueous medium, e. g., water or an aqueous tetrahydrophthalimideI hydrolysis product solution,` whichvv is thereby maintained at a temperature'nearly itsboiling point so as to dissolvethe tetrahydrophthalimide, removing undissolvedV solids, crystallizing theY purified tetrahydrophthalimide' from the aqueous medium, preferably. utilizing the resultant aqueous mother liquor for the furtherpurication. of crudeftetrahydrophthalimide, and. if it is desired to make theY N'-th-iotrichloromethyl` tetrahydrophthalimide;- utilizing the thus purified tetrahydrophthalimide inV the manufactureofthe N thiotrichloromethyl tetrahydrophthalimide.

The crude tetrahydrophthalimidefmay be prepared' by' a-number ofmeans.v One of the-better ways is byreactiony between maleic anhydride andbutadiene. The butadiene'vapors vare passed countercurrently upwardly through downflowing molten maleic anhydride, yielding tetrahydrophthalic anhydride. The latterV in` the molten state is then passed downwardly countercurently toupwardly rising ammonia vapors. The product is then heated tof-maintain the residue inthe molten state and to drive off ammonia and Water so 4as 13o-'yield` the'desired tetrahydrophthalfimides. The molten tetrahydrophthalimide is thus obtained by Whichevervprocess is utilized for its preparation and has. a meltingA point of .1*35-o to 136? C. Y

There are several.V possible vvariations in. the preparation of tetrahydrophthalimides.,..Thus

maleic anhydride can be dissolved in a solvent such as benzene and the butadiene bubbled into it. This is done in a stirred reactor with a cooling jacket and the use of excess butadiene. The tetrahydrophthalic anhydride is isolated and dissolved in ammonium hydroxide to form the ing zone 4 containing water which has been heat- Y ed to below its boiling point. The hot tetrahydrophthalimide melt is preferably sprayed as a finely-divided stream through nozzle 3 and raises the temperature of the water in quench zone 4 to near its boiling point. Any steam formed goes overhead through line 5. The amount of water employed in quench zone 4 and its initial temperature are chosen so as to minimize steam formation. A slight pressure in quench zone 4 also prevents excessive steam formation at temperatures slightly above the boiling point of water.

The aqueous mixture withdrawn through line 6 to pressure leaf iilter 1 consists of an aqueous solution of tetrahydrophthalimide, water-soluble impurities, and water-insoluble impurities, and is maintained at approximately theV same temperature as in quench zone 4. The water-insoluble impurities are removed from the aqueous mixture in pressure leaf lter 1 as sludge through line 8. The residual aqueous filtrate is withdrawn from pressure leaf lter 1 through line 9 VAto cooler I D Where it is cooled and circulated rapidly and then withdrawn tolholding drum II through line I2. Holding drum II is agitated by stirrer I3.

The aqueous filtrate is cooled to approximately atmospheric temperature, e. g., to 35 C., at which point the tetrahydrophthalimide precipitates out, while the water-soluble impurities remain in solution. The slurry of tetrahydrophthalimide and water is withdrawn through line I4 to rotary vacuum lter I5 where the precipitate is filtered from the mother liquor. The

tetrahydronhthalimide withdrawn through line l I6 is suicientlv pure for most purposes. Where the N-thintrichloromethyl tetrahydrophthalimide is to be prepared, the tetrahydronhthalimide crsystals can be sent directly to perchloromethvl mercaptan reactor 22. In the latter, the crystals are dissolved in an alkali hydroxide solution and reacted with perchloromethyl mercaptan as discussed above.

' If desired. the crystallized tetrahydrophthalimide containing some water-soluble impurities can be further washed with cool water at atmospheric temperature to further purifv the crystallized product. The water-wash liquid enters rotary lter I5 through line l1. The combined wash liquid and mother liquor withdrawn through line I8 contains some tetrahydrophthalimide `and a major proportion of the water-soluble impurities. Part of this stream is purged 'through line I9 to prevent undesirable buildup.

Line I1 is thus also used as the entry point for i fresh water for the system. The recirculated combined aqueous media are heated to a suitable temperature below the boiling point in heater e'fas discussed below, and returned through line 2| I to quench zone 4. Y

The temperature of the water in the quench zone is high enough, i. e., near its boiling point, so as to completely dissolve the tetrahydrophthalimide and yet low enough so as not to be unduly vaporized and result in excessive hydrolysis of the tetrahydrophthalimide. The temperature of the Water in quench zone 4 is thus in the range of -10'7 C., and preferably in the range of -104 C. The use of pressure in quench zone 4 permits of higher temperatures but at the cosi of tetrahydrophthalimide hydrolysis.

The temperature of the water in quench zone 4 is attained by the utilization of the heat of the incoming molten tetrahydrophthalimide. The incoming Water is heated, if necessary, in heater 2U only sumciently to bring it up to the desired level utilizing the heat of the molten tetrahydrophthalimide as the major source of heat. At the preferred temperature range indicated, two pounds of Water per pound of imide contained in the crude product is approximately sufficient to remove all the soluble materials usually present from the crude imide. In general, one to three pounds of water at this temperature range is necessary for the complete solubility of the tetrahydrophthalimide puried by this process.

The amount of aqueous solution `purged through line I9 is adjusted so as to maintain the concentration of water-soluble products contained therein substantially below their saturation point, i. e., 10 wt. per cent or less. This latter object is attained by the indicated purging as well as the addition of fresh water in line II.

The variation of tetrahydrophthalimide solubility with temperature can be seen from the fact that at 88 C., a 31.4 wt. per cent solution of tetrahydrophthalimide in water is obtained. while at 26 C. only about a 1.7 wt. per cent solution is obtained. Hence, the solution needs to be cooled to approximately only room temperature to precipitate out the major proportion of dissolved tetrahydrophthalimide.

The water-insoluble impurities removed from 'the crude imide are highly complex and apparently polymeric in nature. It is predominantly this material which apparently causes the poisoning of the N-thiotrichloromethvl tetrahydrophthliamide reaction discussed above.

The water-solubleimpurities remaining in the mother liquor after crystallization ofthe tetrahydrophthalimide at atmospheric temperature are tetrahydrophthalic acids, amides, acid amides, and similar compounds. These can be recovered, if desired, along with dissolved tetrahydrophthalimide bv evaporation of the filtrate removed through line I9. These materials can be considered 'broadly as tetrahvdrophthalimide hydrolysis products. Thus While the crude tetrahvdrophthalimide melt is dissolved initially in Water, subsequent batches of the imide are conveniently dissolved in unsaturated solutions of the hydrolysis products. If these unsaturated solutions are available to begin with, the crude tetrahydrophthalimide may be dissolved initially in these solutions. v

The purified tetrahydrophthalimide obtained by the process of this invention exhibits none of the poisoning activity discussed above and therefore reacts readily with perchloromethyl mercaptan by the methods listed to obtain high yields of N-thiotrichloromethyl tetrahydrophthalimide.

The improved method of this invention is illustrated in the following examples.

. EXAMPLEI Ahotl melt of 1 crudey tetrahydrophthalimide of 94.5%purity at a temperaturelotiabout2329 C. and` comprising about 100; poundsL tetrahydroplithalimide, 5 pounds of soluble-impurities, and 1 pound insoluble impurity, isv pumpedin a ne stream into a vessel simultaneouslyyfed with. an aqueous' solution containing about. 200 pounds of water, about' 4 pounds of. dissolved tetrahydrophthalimide, and` about 11 pounds of soluble hydrolysis products. Thefentering water isza't a temperatureof approximately 60? C. and its'temperature is raised by theVV incoming tetrahydrophthalimide melt to about 939 C... The tetrahydrophthalimide and soluble impurities-ldissolvein the hot solution, andtheinsoluble'impurities arer removed byhot filtration at. approximately 93 C.

The-'solution is then cooled rapidly; to atmospheric temperature, e. g., 29 C., atl Whichpoint most of the tetrahydrophthalimide.crystallizes out. The crystallized tetrahydrophthalimide-is then Washed with 100 pounds of cool Water at atmospheric temperature. The combined mother liquor solutionfrom the tetrahydrophthalimide crystallization and Wash liquid is then purged to remove a solution containing 80 pounds of water, 4.5 pounds of'solublev impurities, and 1.7 pounds of' tetrahydrophthalimide. The'residual 200 pounds of Water, which: is.at'29 C.. and contains dissolved at equilibrium 11 pounds o soluble impurities and 4.3 pounds of tetrahydrophthalimide, is heated to 60 C.- This heated'solution isthen recycledto removefadditional impurities from further quantities of crude tetrahydrophthalimide. The entering hot melt of crude tetrahydrophthalimide raises the temperature of this aqueous solution to about 93 C., which is within the desired range.

The tetrahydrophthalimide product obtained from the crystallization and Water-washing consists of 98 pounds of pure tetrahydrophthalimide, 20 pounds of Water, and 1/2 pound of soluble impurity. This product can be dehydrated if desired and is over 99% pure.

EXAMPLE II A crude tetrahydrophthalimide Was employed in the manufacture of N-thiotrichloromethyl tetrahydrophthalimides. The tetrahydrophthalimide was dissolved in sodium hydroxide and reacted With admixed perchloromethyl mercaptan. A yield of 70% Was obtained.

EXAMPLE III Another batch of the crude tetrahydrophthalimide from the same source as in Example II was purified according to the process of this invention and then reacted to form N-thiotrichloromethyl tetrahydrophthalimide in the same manner as in Example II. A yield of 91.5% was obtained, or an increase of over 30% over the yield of Example II.

This illustrates the great improvement in yield resulting from the purification process of this invention.

EXAMPLE IV A batch of puried tetrahydrophthalimide purified in the same manner as in Examples I and III above, was reacted in exactly the same manner as in Example III to form N-thiotrichloromethyl tetrahydrophthalimides except that 1 to 2 Wt. per cent (based on tetrahydrophthalimide used) of the Water-insoluble impurities, obtainedy by the firstA ltrationy after' Was'decreased up to20%, compared to the yield of Example III. This indicates that the decrease in yield of N-thiotrichloromethyl tetrahydrophthalimide with crude tetrahydrophthalimide is due to a positive poisoning effect rather than1 the mere decrease inconcentration of the active' reactant.

TheY process of this invention is' applicable-to .the purification` ofv other tetrahydrophthalimidesv such as endomethylene tetrahydrophthalimide; and other products obtained from condensation vof a1 diene and maleic anhydride followed'A by condensation with ammonia (or example; the imide of the adduct of isoprene With maleicarhydride').

It is' apparent that the-indicated separations obtained by filtration can also be accomplished bya Wide variety of other ltering, settling' and decanting` means.

It is to be understood that the invention isnot limited to the speci'c examples -Which have been offered merely as illustrations and thatmodifications' may be made without departingY from-the spirit of this invention.

l What isl claimed is:

l. A process for the purication of tetrahydrophthalimides which comprises the steps of 'injecting crude molten tetrahydrophthalimide into water in a quench Zone, the'initial temperature of the water being such that thel higher temperature towhich'the Water 'is-raised"by heat transfer from the molten tetrahydrophthalimide is high enough to effect solution of substantially all the tetrahydrophthalimide but low enough so that the major proportion of the water is maintained in the liquid phase; filtering the resulting aqueous solution maintained at approximately the same temperature as in the preceding step so as to remove Water-insoluble impurities therefrom and cooling the residual aqueous filtrate to approximately 15 to 35 C. to crystallize the tetrahydrophthalimide out of solution.

2. A process as in claim 1, including the additional step of washing the crystallized tetrahydrophthalimide with water at approximately 15 to 35 C.

3. A process as in claim 2, including the additional step of combining the resultant mother liquor from the tetrahydrophthalimide crystallization step with the aqueous Wash liquid from the tetrahydrophthalimide washing step and recycling the combined aqueous media to the quench zone for the further purication of crude tetrahydrophthalimide.

4. A process as in claim 1 in which the higher temperature of the water after heating by the crude tetrahydrophthalimide in the quenching zone is in the range of -104 C`. and the amount of Water in the quenching zone is in the range of about 1 to 3 pounds of Water to 1 pound of tetrahydrophthalimide in the crude tertahydrophthalimide.

5. A process for the purification of tetrahydrophthalimides which comprises the steps of supplying to a mixing zone a stream of crude, molten tetrahydrophthalimide at a temperature in the range of 204260 C.; supplying to said mixing zone a stream of Water at a temperature of below 65 C., said water being in an amount and under such pressure that its temperature is raised to a temperature in the range of 65-107 C. by direct heat transfer from the molten tetrahydrophthalimide While being maintained predominantly in the liquid phase; withdrawing the resulting tetrahydrophthalimide solution and separating water-insoluble impurities therefrom at a temperature approximately the same as in the mixing Zone and cooling the thus separated solution to 15 to.35 C. to crystallize the tetrahydrophthalimide out of solution.

6. A process as in claim in which the temperature of the Water initially supplied to the mixing zone is below 80 C'. and its temperature after being heated by the molten tetrahydrophthalimide is in the range of SDF-104 C.

'7. A process as in claim 6, including the additional step ofy washing the crystallized tetrahydrophthalimide with Water at approximately 15 to 35 C.

8. A process as in claim '7, including the additional step of combining the resultant mother liquor from the tetrahydrophthalimide crystallization step with the aqueous wash liquid from the tetrahydrophthalimide washing step and recycling the combined aqueous media to the mixing zone for the further purification of crude tetrahydrophthalimide.

9. A process for the purification of tetrahydrophthalimides which comprises the steps of supplying to a mixing zone a stream of crude, molten tetrahydrophthalimide at a temperature in the range of 2G4260 C.; supplying to said mixing zone an aqueous stream consisting of an unsaturated solution of tetrahydrophthalimide hydrolysis products at a temperature of below 80 C., said aqueous stream being in an amount ,from the mixing zone and iiltering insoluble impurities therefrom at a temperature approximately the same as in the mixing zone; cooling the residual aqueous iiltrate to 15 to 35 C. to crystallze the tetrahydrophthalimide out of Solution; Washing the crystallized tetrahydrophthalimide with Water at 15 to 35 C.; combining the resultant mother liquor from the tetrahydrophthalimide crystallization step with the aqueous wash liquid from the tetrahydrophthalimide washing step; purging these combined raqueous media so as to maintain the concentration of soluble products contained therein substantially below their saturation point and recycling the purged, residual aqueous media to the mixing zone for further purification of crude tetrahydrophthalimide.

ARTHUR D. GREEN. ERNEST O. OHSOL. ALLEN R. KIT'I'LESON.

REFERENCES CITED The following references are of record in the lle of this patent:

UNITED STATES PATENTS Name Date Jaeger June 20, 1933 Number 

1. A PROCESS FOR THE PURIFICATION OF TETRAHYDROPHTHALIMIDES WHICH COMPRISES THE STEPS OF INJECTING CRUDE MOLTEN TETRAHYDROPHTHALIMIDE INTO WATER IN A QUENCH ZONE, THE INITIAL TEMPERATURE OF THE WATER BEING SUCH THAT THE HIGHER TEMPERATURE TO WHICH THE WATER IS RAISED BY HEAT TRANSFER FROM THE MOLTEN TERTRAHYDROPHTHALIMIDE IS HIGH ENOUGH TO EFFECT SOLUTION OF SUBSTANTIALLY ALL THE TETRAHYDROPHTHALIMIDE BUT LOW ENOUGH SO THAT THE MAJOR PROPROTION OF THE WATER IS MAINTAINED IN THE LIQUID PHASE; FILTERING THE RESULTING AQUEOUS SOLUTION MAINTAINED AT APPROX- 